From 67f455486d2ea20b2d94d6adf5b9b783d079e321 Mon Sep 17 00:00:00 2001 From: NeilBrown Date: Wed, 28 May 2014 13:39:22 +1000 Subject: md/raid56: Don't perform reads to support writes until stripe is ready. MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit If it is found that we need to pre-read some blocks before a write can succeed, we normally set STRIPE_DELAYED and don't actually perform the read until STRIPE_PREREAD_ACTIVE subsequently gets set. However for a degraded RAID6 we currently perform the reads as soon as we see that a write is pending. This significantly hurts throughput. So: - when handle_stripe_dirtying find a block that it wants on a device that is failed, set STRIPE_DELAY, instead of doing nothing, and - when fetch_block detects that a read might be required to satisfy a write, only perform the read if STRIPE_PREREAD_ACTIVE is set, and if we would actually need to read something to complete the write. This also helps RAID5, though less often as RAID5 supports a read-modify-write cycle. For RAID5 the read is performed too early only if the write is not a full 4K aligned write (i.e. no an R5_OVERWRITE). Also clean up a couple of horrible bits of formatting. Reported-by: Patrik Horník Signed-off-by: NeilBrown --- drivers/md/raid5.c | 30 ++++++++++++++++++------------ 1 file changed, 18 insertions(+), 12 deletions(-) (limited to 'drivers/md') diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index ad1b9bea446e..c1e8607d8340 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -292,9 +292,12 @@ static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh, BUG_ON(atomic_read(&conf->active_stripes)==0); if (test_bit(STRIPE_HANDLE, &sh->state)) { if (test_bit(STRIPE_DELAYED, &sh->state) && - !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) + !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) { list_add_tail(&sh->lru, &conf->delayed_list); - else if (test_bit(STRIPE_BIT_DELAY, &sh->state) && + if (atomic_read(&conf->preread_active_stripes) + < IO_THRESHOLD) + md_wakeup_thread(conf->mddev->thread); + } else if (test_bit(STRIPE_BIT_DELAY, &sh->state) && sh->bm_seq - conf->seq_write > 0) list_add_tail(&sh->lru, &conf->bitmap_list); else { @@ -2886,8 +2889,11 @@ static int fetch_block(struct stripe_head *sh, struct stripe_head_state *s, (s->failed >= 1 && fdev[0]->toread) || (s->failed >= 2 && fdev[1]->toread) || (sh->raid_conf->level <= 5 && s->failed && fdev[0]->towrite && + (!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) && !test_bit(R5_OVERWRITE, &fdev[0]->flags)) || - (sh->raid_conf->level == 6 && s->failed && s->to_write))) { + (sh->raid_conf->level == 6 && s->failed && s->to_write && + s->to_write < sh->raid_conf->raid_disks - 2 && + (!test_bit(R5_Insync, &dev->flags) || test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))))) { /* we would like to get this block, possibly by computing it, * otherwise read it if the backing disk is insync */ @@ -3086,7 +3092,8 @@ static void handle_stripe_dirtying(struct r5conf *conf, !test_bit(R5_LOCKED, &dev->flags) && !(test_bit(R5_UPTODATE, &dev->flags) || test_bit(R5_Wantcompute, &dev->flags))) { - if (test_bit(R5_Insync, &dev->flags)) rcw++; + if (test_bit(R5_Insync, &dev->flags)) + rcw++; else rcw += 2*disks; } @@ -3107,10 +3114,10 @@ static void handle_stripe_dirtying(struct r5conf *conf, !(test_bit(R5_UPTODATE, &dev->flags) || test_bit(R5_Wantcompute, &dev->flags)) && test_bit(R5_Insync, &dev->flags)) { - if ( - test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) { - pr_debug("Read_old block " - "%d for r-m-w\n", i); + if (test_bit(STRIPE_PREREAD_ACTIVE, + &sh->state)) { + pr_debug("Read_old block %d for r-m-w\n", + i); set_bit(R5_LOCKED, &dev->flags); set_bit(R5_Wantread, &dev->flags); s->locked++; @@ -3133,10 +3140,9 @@ static void handle_stripe_dirtying(struct r5conf *conf, !(test_bit(R5_UPTODATE, &dev->flags) || test_bit(R5_Wantcompute, &dev->flags))) { rcw++; - if (!test_bit(R5_Insync, &dev->flags)) - continue; /* it's a failed drive */ - if ( - test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) { + if (test_bit(R5_Insync, &dev->flags) && + test_bit(STRIPE_PREREAD_ACTIVE, + &sh->state)) { pr_debug("Read_old block " "%d for Reconstruct\n", i); set_bit(R5_LOCKED, &dev->flags); -- cgit v1.2.3